It is standard practice in the construction industry to test samples of various materials used during construction. This is especially true of concrete, where many field cured specimens are generally required when structural concrete is poured. These specimens are taken from a number of locations across the element or slab when it is poured, and are typically formed as concrete test cylinders.
The American Society for Testing and Materials (ASTM), the American Concrete Institute (ACI), and the American Association of State Highways and Transportation Officials (AASHTO) have developed certain criteria for the formation and testing of concrete test specimens. For examples of such standards see ASTM C 31/C 31M, ACI-301, ACI-318, ASTM C94, and AASHTO T-23. Any deviation from standard testing procedures is grounds for invalidating the obtained test results. Local and national governmental bodies have likewise adopted certain standards for concrete acceptance testing.
One important concrete acceptance testing criteria is that the field cured test specimens represent accurate samples of the cured concrete slab. Concrete curing is an exothermic process (gives off heat) due to the heat released by a hydration reaction which occurs. The build-up of too much heat or the lowering of the temperature beyond proper curing levels can result in concrete strength reduction, cracking, and/or other structural defects. Therefore, the temperature at which the test cylinders are cured is important for the proper testing of concrete. For example, the current ASTM C31/C31M standard specifies a constant curing temperature of 73° Fahrenheit, with a tolerance of ±3° Fahrenheit.
Accordingly, ASTM standards require that field cured concrete specimens, which are cast separately from the concrete slab, be treated during curing to closely approximate the heat developed during the curing process in the more massive concrete slab. If the concrete specimens are not in situ, this is difficult to achieve. Also, the specimens are kept moist until the cure is complete, just as in the case of the poured slab. Any significant variation in the procedure can result in the specimens being an inaccurate representation of the actual qualities of the cast slab they are supposed to represent.
Recently, wet concrete curing boxes have been used to provide stable environments for the curing of concrete test cylinders in situ in order to comply with ASTM standards. The existing curing boxes generally are insulated boxes which have temperature control systems installed in order to heat or cool the inside of the box as needed. The boxes also have a rack to support the test cylinders, which is typically made by bending a sheet of 14 gauge steel into a “U” shape to form the rack, and then forming holes into the top of the rack to allow for water circulation. The rack rests on corner supports extending from the bottom of the prior art curing boxes, and supports the concrete test cylinders submerged under water.
Another recent technological development has introduced the use of “loggers” disposed in the concrete slabs. See, for example, U.S. Pat. No. 6,865,515, the entire contents of which are hereby expressly incorporated herein by reference.
Some prior art wet concrete curing boxes use water pumps having an impeller within a housing above the rack for mixing the water above the rack during the curing process. However, cement dust and other abrasive particles inside the box tend to reduce the service life of the water pumps, which typically results in increased expense and/or delays. Further, curing typically takes about twenty-eight days, which can increase the chance of failure of such prior art water pumps. Additionally, the rack can form a convective barrier which may cause a temperature stratification within the water.
Accordingly, a need exists for a curing box capable of providing reliable in situ concrete test specimens. It is to such a concrete cylinder curing box that the inventive concept(s) disclosed herein is directed.